This invention relates to methods of and apparatus for drawing optical waveguides, and more particularly to the use of laser radiation for heating the waveguide blank to the drawing temperature.
Waveguides used in optical communication systems are hereinafter referred to as "optical waveguides", and are normally constructed from a transparent dielectric material, such as glass or plastic. U.S. Pat. Nos. 3,711,262--Keck and Schultz and 3,775,075--Keck and Maurer describe techniques for making a blank which is heated and drawn into a waveguide having a uniform diameter.
U.S. Pat. No. 3,865,564--Jaeger and Logan suggests the use of laser radiation to heat the waveguide blank to the drawing temperature. The use of laser radiation has many advantages for this purpose. It is uniform, easily controlled and easily focused. In the Jaeger and Logan patent, an annular beam of laser radiation is formed. The annular beam is directed to a conical reflector which focuses the energy on the waveguide blank. A conical reflector is particularly suitable for focusing the energy on the blank. However, with the optical system of this patent, the energy is focused on the axis of the waveguide blank. This results in an inherent instability in the draw. As the glass diameter is reduced, the power density on the surface increases, thus lowering the viscosity and encouraging further diameter reduction. Furthermore, in this patent the blank is heated with a beam which has a power density distribution along the axis of the blank which is the same as the power density distribution of the original laser source. Heating of the blank can be accomplished more efficiently by having the power density highest where the blank diameter has not begun to attenuate.
It is an object of the present invention to provide laser radiation heating which is more stable and more efficient.